Formation of metallic strip material



March 17, 1970 c, OXLEY ET AL 3,501,561

FORMATION OF METALLIC STRIP MATERIAL Filed Dec. 1, 1967 2 Sheets-Sheet 1 IN VEN TOPS DEREK CYfi L UXLEY 6502 5 aid/near STHAPGEON ATTORNEYS March 17, 1970 D. C. OXLEY ET AL FORMATION OF METALLIC STRIP MATERIAL 2 Sheets-Sheet 2 Filed Dec. 1. 1967 INVENTORS DEREK CYR/L OXLEY 050 5 MCIL/HAOYSTZ/RGEON M I: I 1 I ATTORNEYS 3,501,561 FORMATION OF METALLIC STRIP MATERIAL Derek Cyril Oxley, Halfway, near Sheffield, and George McHardy Sturgeon, Dore, Sheflield, England, assignors to The British Iron and Steel Research Association Filed Dec. 1, 1967, Ser. No. 687,378 Claims priority, application Great Britain, Dec. 1, 1966, 53,849/ 66 Int. Cl. B22f 3/02, 3/20 US. Cl. 264111 7 Claims ABSTRACT OF THE DISCLOSURE In a method of forming metallic strip by the compaction of metal powder, which comprises compacting metal powder in the nip between two compacting rolls arranged with their axes parallel in a horizontal plane, to form a self-supporting strip which is withdrawn downwards from the nip, variation in the speed of rolling can be accommodated and production conditions rendered less critical by directing a plurality of liquid or gas jets arranged on either side of the strip into the roll nip.

This invention relates to the formation of metallic strip by the compaction of metal powders.

Metal powders can be formed into strip materials by supplying the powder to the nip of compacting rolls where the powder is subjected to sufficient pressure to form a self-supporting strip and then heat-treating and, if necessary, rolling the strip to obtain the desired mechanical properties. The rolls are suitably arranged with their axes in a horizontal plane with a powder container arranged above them so that the powder is fed into the roll nip by gravity and the compacted powder strip is withdrawn downwards from the nip. The rolling has to be carried out at more than a certain minimum speed which depends primarily on the composition and particle size of the powder and the thickness and density desired in the compacted powder strip, in order to avoid deterioration in strip quality and loss of powder. For example, when using 100 mesh (B.S.) water-atomised stainless steel powder to produce 0.060 inch thick strip having a density of 86% theoretical, the minimum rolling speed is approximately 18 ft. of strip per minute. If the speed is reduced below this figure the powder tends to fall out of the roll nip and strip quality deteriorates. This deterioration takes the form of irregularities in strip width and undesirably large variations in density across the width of the strip. If the rolling speed is reduced even further, conditions are obtained where no strip is produced and only loose powder falls away from the rolls.

We have found that for a given set of powder and strip parameters, strip having good properties can be produced at rolling speeds lower than the minimum rolling speed referred to above by setting up a resistance to powder flow through the roll nip by means of a plurality of liquid or gas jets arranged on each side of the strip and directed into the roll nip.

Thus, our improved method of strip formation comprises compacting metal powder in the nip between two compacting rolls arranged with their axes parallel in a horizontal plane, to form a self-supporting strip which is withdrawn downwards from the nip, while directing a plurality of liquid or gas jets arranged on either side of the strip into the roll nip.

The main advantages of this procedure are that the production of sound strip is assisted at the low speeds used when starting and stopping the compaction mill and that the mill can be run at lower speeds when threading up a continuous rolling and sintering plant. The invention also nited States Patent permits larger roll gap settings to be used for a given rolling speed or, alternatively enables a more highly flowable powder to be used with a given roll gap at a given rolling speed.

Apparatus for carrying out our new process comprises (i) a pair of compacting rolls arranged with their axes parallel to each other in a horizontal plane, (ii) a powder container above the nip of the rolls for feeding powder into the nip, and (iii) two sets of nozzles, one set being arranged on each side of a vertical plane passing through the roll nip and each nozzle being arranged to direct a liquid or gas jet into the nip. Preferably the nozzles are arranged in two lines, one on each side of said vertical plane and parallel thereto. Instead of using a plurality of jets on each side of the emerging strip, a single fluid knife as supplied from a slotted manifold which extends across the width of the strip, may be provided on each side of the emerging strip, the two fluid knives being directed into the roll nip.

The apparatus may, and preferably does, additionally comprise side guides positioned at each end of the powder container and extending into the nip which serve to reduce or prevent sideways spread of the powder and thus to define the width of the strip produced. Such side guides take the form of suitably shaped plates. Instead of using such mechanical guides, the apparatus may be provided with a nozzle at each end of the powder container, each nozzle being arranged to direct a liquid or gas jet into the nip. The jets are suitably directed substantially normal to the horizontal plane containing the roll axes and their effect is to erode away and disperse powder which spreads sideways beyond the limits set by the distance between the jets so that a strip of substantially uniform width is obtained.

Further features and advantages of the invention will become apparent from the following description of a preferred method and apparatus for powder compaction, given by way of example only, with reference to the accompanying drawings in which:

FIGURE 1 is an end elevation of a powder compaction apparatus in use; and

FIGURE 2 is a perspective view of the underside of the compacting rolls of the apparatus shown in FIGURE 1, showing the disposition of the gas jets, the emerging strip being omitted for clarity.

FIGURE 3 is a perspective view similar to FIGURE 2 but showing a slotted manifold on each side of the roll nip for delivering the fluid stream in the form of a fluid knife into the nip.

Referring to the drawings, the apparatus comprises a pair of axially-parallel horizontal compacting rolls 10 and 11, the nip between the rolls being designated 12. The rolls are connected to a suitable drive mechanism (not shown). A powder container 13 is positioned above the rolls, the lower part of the container extending downwards almost into the nip 12 and being suitably shaped for this purpose. The container is open at the bottom and the powder falls through the open bottom and is compacted by the rolls as it enters the nip. The compacted strip 14 leaves the rolls in a downward direction indicated by arrow 15'.

The strip width is controlled by a side guide plate 17 at each end of the nip, each guide plate fitting closely alongside the end of each roll.

A tubular gas manifold 18 fitted with a number of short open-ended pipes 19 is disposed below each roll and each gas manifold is connected to a supply of gas (not shown) by gas hoses 20. The manifolds are positioned so that the gas jets from pipes 19 are directed into the roll nip on either side of the emerging strip. The gas jets tend to reduce powder flow through the roll gap and by suitable adjustment of the gas pressure, loose powder can be prevented from falling out of the gap. The gas employed will normally be compressed air.

In the embodiment shown in FIGURE 3 a slotted manifold 21 is provided on each side of the formed strip. Fluid in the form of a continuous fluid knife or sheet extending across the width of the formed strip issues from the elongated slot 22 of each manifold 21 and into the roll nip.

The use of gas rather than liquid jets is preferred because gases do not, of course, wet the strip as do liquids, and are generally more convenient.

Using the apparatus shown in the drawings we have produced good quality 0.060 inch thick strip from 100 mesh (B.S.) \vater-atornised stainless steel powder at rolling speeds of 5 ft. of strip per minute, at strip densiites of 86% theoretical with a density variation along the strip width of i2%. This strip was in all respects as good as the strip which is produced at rolling speeds over 18 ft./min. without the gas jets on either side of the strip.

In another test, using 7 /2 inch diameter compacting rolls with a roll gap setting of 0.015 inch, water-atomised stainless steel powder of size 30 mesh to dust, was compacted. It was possible to reduce the minimum rolling speed from 18 ft./min. to 2 ft./min. by having a pair of air jets on each side of the strip directed upwardly towards the sides of the strip. The nozzles of the air jets were 0.060 inch internal diameter, and the air pressure was 20 pounds per square inch.

The flow of powder into the roll gap will depend on the exact positions of the gas jets, the gas pressure used and the size of the jet nozzles. It will also depend on the powder density, particle shape, size distribution, roll gap setting and roll diameter. It is therefore impossible to specify, for example, particular gas pressures which may be used since these are dependent on many other factors.

We claim:

1. A method of forming a self-supporting metallic strip by roll compacting metal powder, comprising (a) feeding said metal powder into the roll gap and nip of a pair of rotating compacting rolls having parallel axis in a horizontal plane, and (b) directing a fluid jet stream located on each side of the formed strip and extending across the width of the formed strip on each side thereof into said nip of the rotating rolls to permit forming said metallic strip at a rolling speed below the minimum rolling speed at which powder tends to fall out of the roll nip in the absence of the jet stream, while preventing the falling of loose metal powder from said roll gap during said rolling.

2. The method of claim 1 wherein the fluid jet stream on each side of the formed strip is composed of a plurality of individual jet streams.

3. The method of claim 2 wherein the fluid jet stream on each side of the formed strip is in the form of an elongated continuous sheet.

4. The method of claim 1 wherein the fluid of the jet stream is a gas.

5. The method of claim 1 wherein the fluid of the jet stream is a liquid.

6. The method of claim 1 in which step (b) permits forming said metallic strip at a rate of about 5 ft. per minute.

7. The method of claim 1 in which step (b) permits forming said metallic strip at a rate of about 2 ft. per minute.

References Cited UNITED STATES PATENTS 3,162,708 12/1964 Lund et al. 264-111 3,235,954 2/1966 Fromson 264-111 FOREIGN PATENTS 251,285 5/ 1963 Australia.

ROBERT F. WHITE, Primary Examiner J. R. HALL, Assistant Examiner US. Cl. X.R. 18-2; l64277 

